First off, it is not kagami uchiha, why? Because when tobi fought the yondaime, he got injured and leaked zetsu like material.
Therefore, this chapter only strengthens the theory that tobi is in fact a zetsu clone, of who we don't know. It could very well be Madara (zetsu clone) and I truly believe this theory now more than ever.
This is why.
Firstly, he has the intent... To use a genjutsu to rule the world. (power hungry)
2. Zetsu has the ability to clone shinobi to their exact chakra, maybe he did the same with madara.
3. This explains why kurama felt tobi's presence as Madara when he got extracted from kushina.
4. Madara (real one) obviously knows who tobi is, they had a plan together remember? So maybe he had zetsu recreate himself near his death bed, so that he may enact the plan.
5. we now know Tobi knows all, just like zetsu knows all, kinda weird huh?
Anyway, I never liked this theory, in fact I was more level with the izuna one more. however, after today, this chapter has made the Madara zetsu clone the front-runner imo.
Also we know nothing about zetsu, yet he has played a big role so far, so I mean we're kinda overdue for a back-story on him, don't you think?